Out of Africa: clues to dinosaur evolution.

Paleontologists searching remote reaches of the Sahara have discovered the remains of two new species of dinosaurs that may help solve the mystery of how these reptiles evolved and when the continents separated. Paul C. Sereno of the University of Chicago led the team of researchers that uncovered the findings on a 4-month expedition to central Niger in 1993. They describe their discovery in the Oct. 14 SCIENCE.

Sereno's team found the remains of a meat-eating dinosaur, known as a theropod, that stretched 27 feet from head to tail and the partial skeleton of a four-legged, plant-eating dinosaur known as a sauropod. According to Sereno, both lived approximately 130 million years ago, during the Cretaceous period.

The researchers named the theropod Afrovenator abakensis and suggest that it resembles Allosaurus, a dinosaur that roamed North America about 150 million years ago. The new sauropod also may be related to a North American dinosaur of that period, Camarasaurus. The sauropod remains unnamed, awaiting the excavation of a more complete skull, Sereno explains.

What are these relatives of North American dinosaurs doing in the Sahara? In search of the answer, Sereno turned to the prevailing idea of how the continents separated. This theory holds that a supercontinent known as Pangaea covered most of Earth 300 million to 200 million years ago.

Pangaea began fragmenting into northern (Laurasia) and southern (Gondwana) landmasses about 180 million years ago; further separation of these landmasses into continents followed. With this in mind, Sereno expected African dinosaurs from 130 million years ago to look quite different from their northern counterparts yet similar to their contemporaries on the partially connected South American continent.

His team discovered the opposite. The African dinosaurs bear a closer resemblance to species from North America, Asia, and Europe, which made up the northern landmass, than to species found in South America.

"This means multiple theropod and sauropod groups had evolved and spread worldwide before the northern and southern landmasses had completely separated," Sereno says. "The presence of these dinosaurs may indicate that the southern landmass was not isolated [from Laurasia] for as long as we previously thought and that the continents may have been connected longer than most people think."

Other researchers, while acknowledging the importance of Sereno's findings, view his ideas about the timing of continental separation with caution.

"The good news is that Sereno and his team found such a reasonably complete dinosaur specimen in Africa," says Philip J. Currie of Canada's Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta. "There is so little we know about meat-eating dinosaurs in Africa that this is an important first step in putting the story together."